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Localized-itinerant electronic transition in the perovskite system La 1 − x <mml:mi mathvariant="…

1995; American Physical Society; Volume: 52; Issue: 12 Linguagem: Inglês

10.1103/physrevb.52.8776

1095-3795

Hoan C. Nguyen, John B. Goodenough,

Transition Metal Oxide Nanomaterials

The insulator-metal (I-M) transition near the critical composition ${\mathit{x}}_{\mathit{c}}$\ensuremath{\approxeq}0.26 in ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{VO}}_{3}$ is confirmed, as is the apparent existence of a solid solution over the entire compositional range 0\ensuremath{\le}x\ensuremath{\le}1 according to room-temperature powder x-ray diffraction. Although interpretation of the evolution with x of its physical properties would seem to require a global electronic model, the magnetic and transport properties we measure below room temperature suggest the presence of a two-phase electronic model with itinerant-electron behavior in hole-rich (or electron-poor) domains and localized-electron behavior in hole-poor domains. Localized electronic states within the itinerant-electron domains are associated with atomic vacancies or lattice defects. The system may remain atomically disordered, but an electronic phase segregation can be accomplished at lower temperatures by cooperative oxygen-atom displacements. Separation into electronically distinguishable phases by this mechanism would not be detected easily by powder x-ray diffraction. A first-order structural phase transition occurs in the interval 400--640 K for all x; the high-temperature phase exhibits a Curie-Weiss paramagnetism.